In connection with the control of internal combustion engines, at least one performance quantity is often limited to a predefined maximum value to protect the internal combustion engine or the components, for example, or to restrict the driving performance of the vehicle, among others. Pertinent examples are speed restrictions, torque limitations or driving speed restrictions. As a rule, the intention is to observe the limit value to the greatest possible extent and to comfortably control the performance quantity to the limit value, without overshoots. One such example is a maximum speed limitation of an internal combustion engine from German Patent Application No. 195 06 082 in which, beginning with a starting value below the limit value, the throttle-valve angle is reduced in a step-wise manner in order to avoid a speed overshoot beyond the limit value.
Another realization of a speed limitation is referred to in German Patent Application No. 33 19 025. Here, in response to the limit value being exceeded, the ignition angle is adjusted and/or the air-fuel mixture made leaner by a corresponding adjustment of the injection time in an attempt to restrict the speed to the limit value.
In some applications, when the limiting is realized by controlling the air supply via a throttle valve, for example, this may result in an oscillation tendency because of the dead time of the controlled system and/or due to the sudden torque reduction, in particular while the performance quantity is adjusted to the limit value. When the ignition-angle adjustment is used as the limiting actuating variable, the exhaust gas becomes very hot due to the ignition angle being delayed and may therefore possibly damage the catalytic converter and/or other components in the region of the exhaust-gas tract. Consequently, there is a need to optimize a limiting function.